Rubber composition with precipitated silica partially pre-hydrophobated with alkylsilane coupled to an elastomer in situ within the rubber composition and tire with component

ABSTRACT

The invention relates to a rubber composition containing diene based elastomer(s) coupled with a silica coupler in situ in the rubber composition to a precipitated silica which is partially pre-hydrophobated with an alkylsilane comprised of an alkoxyalkylsilane, its preparation and to a tire containing a component comprised of such rubber composition.

FIELD OF INVENTION

The invention relates to a rubber composition containing diene basedelastomer(s) coupled with a silica coupler in situ in the rubbercomposition to a precipitated silica which is partiallypre-hydrophobated with an alkylsilane, its preparation and to a tirecontaining a component comprised of such rubber composition.

BACKGROUND OF THE INVENTION

Vehicular tires may be prepared with a component of a rubber compositionwhich contains reinforcing filler comprised of a combination ofprecipitated silica and rubber reinforcing carbon black. Theprecipitated silica is usually provided with a silica coupling agent(silica coupler) to enhance its rubber reinforcement by couplingprecipitated silica to a conjugated diene based elastomer contained inthe rubber composition.

Precipitated silica is generally hydrophilic in nature and therefore hasa greater affinity to itself, namely to other hydrophilic precipitatedsilicas, with less affinity to a diene-based elastomer in a rubbercomposition which, in turn, makes it difficult to obtain a satisfactorydispersion of the precipitated silica throughout the rubber composition.Such difficulty of obtaining a dispersion of hydrophilic precipitatedsilica is well known to those having skill in such art.

In practice, the precipitated silica may be hydrophobated to promote agreater affinity to a diene based elastomer in a rubber composition andto thereby enable a more satisfactory dispersion of precipitated silicain a rubber composition.

The precipitated silica may be hydrophobated, for example, with analkylsilane in a form of, for example, a halogenated alkylsilane oralkoxyalkylsilane to react with hydroxyl groups on the precipitatedsilica. It may also be hydrophobated with a silica coupling agent wherethe coupling agent contains a moiety (e.g. alkoxysilane moiety) to reactwith hydroxyl groups on the silica and another different moiety (e.g.polysulfide moiety) interactive with the diene-based elastomer(s) of therubber composition to thereby render the precipitated silica morereadily dispersible in the rubber composition.

Precipitated silica may be pre-hydrophobated prior to its introductioninto the rubber composition or may be in situ hydrophobated within therubber composition.

However, it is readily seen that such pre-hydrophobation of theprecipitated silica with an alkylsilane (by way of a reaction with ahalogenated alkyl silane or alkoxysilane) can render the hydrophobatedprecipitated silica significantly unreactive, or only minimallyreactive, with a subsequent addition of silica coupling agent. Suchpre-hydrophobation thereby eliminates a significant portion of hydroxylgroup sites on the precipitated silica available to subsequently reactwith a silica coupling agent which is added subsequently in situ withinthe rubber composition. Therefore, while such pre-hydrophobationpromotes dispersion of the precipitated silica in the rubbercomposition, it can prevent significant subsequent coupling of theprecipitated silica to a diene-based elastomer contained in a rubbercomposition with a silica coupling agent.

Exemplary of hydrophobation of precipitated silica, and not intended tobe limiting, may be found, for example, U.S. Pat. Nos. 4,474,908,5,780,538 and 6,573,324.

For this invention, it is desired to evaluate dispersion(dispersability) of precipitated silica in a rubber compositioncontaining a diene-based elastomer followed by coupling of the dispersedprecipitated silica to a diene based elastomer contained in the rubbercomposition to thereby both promote stabilization of the dispersedprecipitated silica within the rubber composition and to promotereinforcement of the rubber composition.

To enable such combination, it is desired to evaluate partiallypre-hydrophobating a precipitated silica to promote its dispersabilityin the rubber composition while promoting a significant retention ofresidual unreacted hydroxyl groups on the precipitated silica followedby coupling the dispersed partially pre-hydrophobated precipitatedsilica by reaction of its residual hydroxyl groups with a silanecontaining (e.g. alkoxysilane containing) silica coupling agent in situwithin a rubber composition which contains a conjugated diene basedelastomer.

It therefore is desired to provide such partial pre-hydrophobation ofprecipitated silica with the alkylsilane exclusive of silica couplingagent during such pre-hydrophobation to prevent an inherent competitionof the alkylsilane with silica coupling agent for hydroxyl groups on theprecipitated silica during such partial pre-hydrophobation.

While such partial pre-hydrophobation of precipitated silica to promoteits dispersibility combined with a subsequent and separate coupling witha coupling agent to a rubber composition may appear to be relativelystraight forward in nature, it is however believed an innovativemethodology and resultant product of this application is a significantdeparture from past practice. (for example, see U.S. Pat. Nos.6,573,324, 6,830,811 and 7,569,107), where hydrophobation of aprecipitated silica was provided with a combination of alkylsilane andsilica coupling agent.

The partial pre-hydrophobation of the silica surface with an alkylsilaneprior to the in-situ addition of the coupling agent allows for simpledispersion of the partially pre-hydrophobated silica within the rubbermatrix prior to coupling of that pre-hydrophobated silica with therubber matrix with the silica coupler through residual hydroxyl groupsremaining on the precipitated silica after its pre-hydrophobation. Thesubsequent reaction of a silica coupler is provided to stabilize thedispersed pre-hydrophobated silica within the rubber as well as toreinforce the rubber itself by reaction of the added silica coupler withavailable and accessible residual hydroxyl (e.g. silanol) groupscontained on the pre-hydrophobated silica, and which may also becontained on the pre-hydrophobating alkylsilica compound and with thediene based elastomer of the rubber composition.

For this evaluation, it is desired to partially pre-hydrophobate aprecipitated silica by reaction of an alkylsilane, in a form of ahalogenated alkylsilane or an alkoxyalkylsilane compound. By suchpartial pre-hydrophobation, it is desired that a significant content ofresidual unreacted hydroxyl groups on the precipitated silica remainsavailable for subsequent reaction with a silica coupling agent in situwithin a rubber composition and to thereby couple the precipitatedsilica to a conjugated diene elastomer contained in a rubbercomposition.

By such methodology, it is envisioned that dispersion of theprecipitated silica in the rubber composition is promoted, followed bystabilization of the dispersed precipitated silica in the rubbercomposition and reinforcement of the rubber composition by the dispersedpre-hydrophobated precipitated silica is provided.

It therefore is desired to provide such partial pre-hydrophobation ofprecipitated silica with the alkylsilane exclusive of silica couplingagent during such pre-hydrophobation to prevent an inherent competitionof the alkylsilane with silica coupling agent for hydroxyl groups on theprecipitated silica during such pre-hydrophobation.

In the description of this invention, the term “phr” relates to parts byweight for a material or ingredient per 100 parts by weightelastomer(s)”. The terms “rubber” and “elastomer” are usedinterchangeably unless otherwise indicated. The terms “cure” and“vulcanize” are used interchangeably unless otherwise indicated.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention a method is provided which comprises:

(A) providing a dispersion of a partially pre-hydrophobated aprecipitated silica in a rubber composition containing at least oneconjugated diene based elastomer, wherein said partiallypre-hydrophobated precipitated silica is prepared by:

-   -   (1) reacting a halogenated alkylsilane or an alkoxyalkylsilane        with a portion of hydroxyl groups on a precipitated silica to        thereby provide a partially pre-hydrophobated precipitated        silica containing residual (unreacted) hydroxyl groups and        blending said partially pre-hydrophobated precipitated silica        with a rubber composition containing at least one conjugated        diene based elastomer to provide a dispersion thereof in said        rubber composition, or    -   (2) blending a precipitated silica with a rubber composition        containing at least one diene based elastomer to provide a        dispersion thereof in said rubber composition and reacting said        dispersed precipitated silica with an alkoxyalkylsilane in situ        within said rubber composition to thereby provide a partially        pre-hydrophobated precipitated silica

(B) stabilizing said dispersion of partially pre-hydrophobatedprecipitated silica within said rubber composition and reinforcing saidrubber composition by reacting a silica coupling agent with saidresidual hydroxyl groups of said partially pre-hydrophobatedprecipitated silica in situ within the rubber composition subsequent toand thereby separate from said partial pre-hydrophobation of saidprecipitated silica with said halogenated alkylsilane oralkoxyalkylsilane, wherein said silica coupling agent contains a moietyreactive with said residual hydroxyl groups of said partiallypre-hydrophobated precipitated silica and another different moietyinteractive with said conjugated diene based elastomer(s) of said rubbercomposition;

wherein the alkyl silane (compound) for pre-hydrophobation of saidprecipitated silica is of the general Formula (I)X_(n)—Si—R_(4-n)   (I)

wherein R is an alkyl radical having from 1 to 10, alternately from oneto 8, carbon atoms such as, for example, methyl, ethyl, isopropyl,n-butyl, octyl and octadecyl radicals, n is a value of from one to threeand X is a radical selected from halogen, particularly comprised ofchlorine or bromine, preferably a chlorine radical, and alkoxy radicalsor groups, wherein said alkoxy radical is (R¹O)—, wherein R¹ is an alkylradical comprised of from 1 to 3 carbon atoms such as, for example,methyl, ethyl and isopropyl radicals, of which at least one of which isdesirably an ethyl radical. Said halogenated alkylsilane is desirably achlorinated alkylsilane.

The amount of the halogenated alkylsilane or alkoxyalkylsilane for saidpartial pre-hydrophobation of the precipitated silica may be estimated,for example, by calculating the number of surface hydroxyls on thesilica. Precipitated silicas are shown to have approximately 4.6 to 4.9hydroxyl groups per square nanometer of surface area, independent of thesurface area and structure of the silica (L. T. Zhura: Colloids andSurfaces, A: Physicochem. Eng. Aspects 173 (2000) 1 through 38). Forexample, 1 gram of silica with a surface area of 160 meters²/gram wouldhave 1.6×10²⁰ square nanometers of surface area. This would relate to7.36×10²⁰ hydroxyl groups or 1.22×10⁻³ moles of hydroxyl groups. It isassumed that one halogenated or alkoxy group of the hydrophobatingalkylsilane compound will react with the surface area of the silica,therefore, on this basis, the amount of hydrophobating compound (thehalogenated alkylsilane or alkoxyalkylsilane) to be added is less than1.22×10⁻³ moles of hydrophobating compound per gram of silica.

As indicated, in one embodiment, the precipitated silica is partiallypre-hydrophobated by reaction with a halogenated alkylsilane oralkoxyalkylsilane to form a composite thereof prior to its addition to arubber composition containing a diene based elastomer(s).

As indicated, in one embodiment, the precipitated silica is partiallypre-hydrophobated by reaction with an alkoxysilane to form a compositethereof in situ within a rubber composition containing a diene basedelastomer(s).

In further accordance with this invention, a rubber composition isprovided prepared by said method, particularly a sulfur cured rubbercomposition.

In additional accordance with this invention, a rubber composition isprovided comprised of, based on parts by weight per 100 parts by weight(phr) of conjugated diene based elastomer,

(A) at least one conjugated diene-based elastomer,

(B) about 10 to about 120, alternately about 40 to about 100, phr ofreinforcing filler comprised of a combination of rubber reinforcingcarbon black and precipitated silica comprised of:

-   -   (1) up to about 60, alternately up to about 15, phr of rubber        reinforcing carbon black, and    -   (2) precipitated silica comprised of:        -   (a) partially pre-hydrophobated precipitated silica with an            alkylsilane comprised of halogenated alkylsilane or            alkoxyalkylsilane where said partially hydrophobated            precipitated silica contains residual (unreacted) hydroxyl            groups, and        -   (b) optionally up to about 30, alternately optionally up to            about 20, phr of precipitated silica (precipitated silica            which is not pre-hydrophobated), and

(C) silica coupling agent having a moiety (e.g. alkoxysilane) reactivewith said residual hydroxyl groups on said partially pre-hydrophobatedprecipitated silica and another different moiety (e.g. polysulfide ormercapto based moiety) interactive with said diene-based elastomer(s),

wherein said alkyl silane for pre-hydrophobation of said precipitatedsilica is of the general Formula (I)X_(n)—Si—R_(4-n)   (I)

wherein R is an alkyl radical having from 1 to 10, alternately from 1 to8, carbon atoms such as, for example, methyl, ethyl, isopropyl, n-butyl,octyl and octadecyl radicals, n is a value of from 1 to 3 and X is aradical selected from halogen, particularly comprised of chlorine orbromine, preferably a chlorine radical, and from alkoxy radicals,wherein said alkoxy radical is (R¹O)—, wherein R¹ is an alkyl radicalcomprised of from 1 to 3 carbon atoms such as, for example, methyl,ethyl and isopropyl radicals, of which at least one of which isdesirably an ethyl radical.

In one embodiment, said rubber composition is sulfur cured.

Representative various alkyl silanes (alkylsilane compounds) of Formula(I) are, for example, trichloro methyl silane, dichloro dimethyl silane,chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethylsilane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxyoctyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane,triethoxy methyl silane, triethoxy propyl silane, triethoxy octylsilane, diethoxy dimethyl silane, trichlorooctyl silane,trichlorooctadecylsilane, and trichlorpropylsilane.

In further accordance with this invention, a tire of this invention isprovided which contains a component comprised of said rubbercomposition. Representative of such tire component is, for example, atire tread such including at least one of tread cap and/or tread baserubber layer, tire sidewall, tire carcass component such as for examplea carcass cord ply coat, tire sidewall stiffening insert, an apexadjacent to or spaced apart from a tire bead, tire chafer and tire beadcomponent.

It is understood that the tire component may be provided as a sulfurcured rubber composition.

A significant aspect of this invention is providing a rubber compositionwith a combination of a more readily dispersible alkylsilane partiallypre-hydrophobated precipitated silica in the rubber composition whichcontains residual (unreacted) hydroxyl groups which is subsequentlycoupled to a diene-based elastomer in situ in the rubber composition byreaction of a silica coupling agent with said residual hydroxyl groupson said partial pre-hydrophobated precipitated silica wherein thereaction of said coupling agent is separate from, and thereby decoupledfrom, said alkylsilane partial pre-hydrophobation of said precipitatedsilica.

In the practice of this invention, the rubber composition may becomprised of various conjugated diene based elastomers. Such diene-basedelastomers may be polymers and copolymers of conjugated dienes, such as,for example, isoprene and 1,3-butadiene, and copolymers of at least oneconjugated diene hydrocarbon with styrene.

For example, representative of such elastomers are cis 1,4-polyisoprenerubber (natural and synthetic), cis 1,4-polybutadiene rubber, high vinylpolybutadiene rubber having a vinyl 1,2 content in a range of about 10percent to about 90 percent, styrene/butadiene copolymer (SBR) rubber(aqueous emulsion or organic solution polymerization preparedcopolymers) and including organic solvent polymerization prepared SBRhaving a vinyl 1,2-content in a range of about 10 to about 90 percentbased on its polybutadiene derived portion and a polystyrene content ina range of about 10 to about 60 percent based upon the copolymer,styrene/isoprene/butadiene terpolymer rubber, butadiene/acrylonitrilerubber, styrene/isoprene copolymer and isoprene/butadiene copolymerrubber, 3,4-polyisoprene rubber and trans 1,4-polybutadiene rubber.

Organic solvent polymerization prepared tin coupled elastomers such asfor example, tin coupled styrene/butadiene copolymers may also be used.

Tin coupled copolymers of styrene/butadiene may be prepared, forexample, by introducing a tin coupling agent during thestyrene/1,3-butadiene monomer copolymerization reaction in an organicsolvent solution, usually at or near the end of the polymerizationreaction. Such coupling of styrene/butadiene copolymers is well known tothose having skill in such art.

In practice, it is usually preferred that at least 50 percent and moregenerally in a range of about 60 to about 85 percent of the Sn (tin)bonds in the tin coupled elastomers are bonded to butadiene units of thestyrene/butadiene copolymer to create Sn-dienyl bonds such as butadienylbonds.

Creation of tin-dienyl bonds can be accomplished in a number of wayssuch as, for example, sequential addition of butadiene to thecopolymerization system or use of modifiers to alter the styrene and/orbutadiene reactivity ratios for the copolymerization. It is believedthat such techniques, whether used with a batch or a continuouscopolymerization system, is well known to those having skill in suchart.

Various tin compounds, particularly organo tin compounds, may be usedfor the coupling of the elastomer. Representative of such compounds are,for example, alkyl tin trichloride, dialkyl tin dichloride, yieldingvariants of a tin coupled styrene/butadiene copolymer elastomer,although a trialkyl tin monochloride might be used which would yieldsimply a tin-terminated copolymer.

Examples of tin-modified, or coupled, styrene/butadiene copolymerelastomers might be found, for example and not intended to be limiting,in U.S. Pat. No. 5,064,901.

The precipitated silica reinforcement may, for example, be characterizedby having a BET surface area, as measured using nitrogen gas, in therange of, for example, about 40 to about 600, and more usually in arange of about 50 to about 300, square meters per gram. The BET methodof measuring surface area might be described, for example, in theJournal of the American Chemical Society, Volume 60, as well as ASTMD3037.

Representative examples of rubber reinforcing carbon blacks are, forexample, and not intended to be limiting, referenced in The VanderbiltRubber Handbook, 13^(th) edition, 1990, on Pages 417 and 418 with theirASTM designations.

Precipitated silicas are synthetic amorphous silicas such as, forexample, and not intended to be limiting, various commercially availableprecipitated silicas from PPG Industries under the Hi-Sil trademark withdesignations 210, 243, 315 etc., silicas from Solvay with, for example,designations of Zeosil 1165MP and Zeosil 165GR, silicas from Evonikwith, for example, designations VN2 and VN3 and chemically treatedprecipitated silicas such as for example Agilon™ 400 from PPG.

Such precipitated silicas may, for example, be characterized by having anitrogen surface area (BET test) in a range, for example, about 100 toabout 300, and more usually about 130 to about 200 cc/100 g.

Representative of silica coupling agents for the precipitated silica arecomprised of, for example;

(A) bis(3-trialkoxysilylalkyl) polysulfide containing an average inrange of from about 2 to about 4, alternatively from about 2 to about2.6 or from about 3.2 to about 3.8, sulfur atoms in its connectingbridge, or

(B) an organoalkoxymercaptosilane, or

(C) their combination.

Representative of such bis(3-trialkoxysilylalkyl) polysulfide iscomprised of bis(3-triethoxysilylpropyl) polysulfide.

It is readily understood by those having skill in the art that therubber composition of the tread rubber would be compounded by methodsgenerally known in the rubber compounding art, such as mixing thevarious sulfur-vulcanizable constituent rubbers with various commonlyused additive materials such as, for example, curing aids, such assulfur, activators, retarders and accelerators, processing additives,such as oils, resins including tackifying resins and plasticizers,fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants andantiozonants, peptizing agents and reinforcing materials such as, forexample, carbon black. As known to those skilled in the art, dependingon the intended use of the sulfur vulcanizable and sulfur vulcanizedmaterial (rubbers), the additives mentioned above are selected andcommonly used in conventional amounts.

The presence and relative amounts of the above additives are notconsidered to be an aspect of the present invention, unless otherwiseindicated, which is more primarily directed to a tire with a componentof a rubber composition which contains the described particulate, alkylsilane pre-hydrophobated precipitated silica aggregates and silicacoupling agent.

The tires can be built, shaped, molded and cured by various methodswhich will be readily apparent to those having skill in such art.

EXAMPLE I Preparation and Use of Partially Pre-Hydrophobated Silica WithHalogenated Alkylsilane

Partially hydrophobated precipitated silica is prepared by reacting thefollowing halogenated alkylsilanes with precipitated silica throughhydroxyl groups on the precipitated silica as reported in the followingTable A.

TABLE A Precipitated Silicas Halogenated alkylsilane Silica A (notpre-hydrophobated) None Silica B (pre-hydrophobated)Trimethylchlorosilane Silica C (pre-hydrophobated) TrichloropropylsilaneSilica D (pre-hydrophobated) Trichlorooctylsilane Silica E(pre-hydrophobated) Trichlorooctadecylsilane Silica F (commercialtreated silica) Not applicablePreparation of Silica C: Trichloropropylsilane Treated PrecipitatedSilica

Particulate precipitated silica A was obtained as Zeosil 1165MP™available from Solvay. The precipitated silica A in an amount of 440grams was placed in a high speed blender for 3 minutes to break thesilica into less compacted aggregates. A toluene suspension of thesilica particles was prepared in a 2 liter resin kettle equipped with aDean-Stark Trap. The toluene/silica suspension was refluxed withstirring and 21 ml of water was collected by azeotrope which representedabout 4.7 percent by weight of the silica used to prepare thesuspension.

Trichloropropylsilane was added drop-wise in amount of 85 grams to therefluxing suspension to partially hydrophobate the precipitated silicaA. As the trichloropropylsilane was added while stirring the dispersion,the suspension became less viscous, more transparent and assumed anappearance of a solution as the hydrophobation of the precipitatedsilica continued. The stirring continued under reflux conditions for 2hours and the mixture then cooled and filtered. The collected (namelyfiltered) partially hydrophobated silica was used for evaluation inrubber formulations illustrated in the following Table 1 and referred toas “Silica C”.

The precipitated silica C was considered as being partiallyhydrophobated by reaction of the alkyl silane with hydroxyl groups onthe precipitated silica whereby the alkyl groups attached to theprecipitated silica being basically non-reactive and whereby thealkylsilane hydrophobated precipitated silica C itself being onlyminimally reactive to the extent of minimal remaining residual unreactedhydroxyl groups on the precipitated silica.

Silica B Preparation: Trimethylchlorosilane Treated Precipitated Silica

In a similar manner Silica B was prepared by treating (partiallyhydrophobating) 400 grams of the precipitated silica A with 60.5 gramsof trimethylchlorosilane.

Silica D Preparation: Trichlorooctylsilane Treated Precipitated Silica

In a similar manner Silica D was prepared by treating (partiallyhydrophobating) 400 grams of the precipitated silica A with 85 grams oftrichlorooctylsilane.

Silica E preparation: Trichlorooctadecylsilane Treated PrecipitatedSilica

In a similar manner Silica E was prepared by treating (partiallyhydrophobating) 450 grams of the precipitated silica A with 60.5 gramsof trichlorooctadecylsilane.

Preparation of Rubber Compositions (Rubber Samples)

Rubber compositions (referred to herein as rubber Samples A through E),were prepared which contained the untreated precipitated silica A(Control rubber Sample A) and treated (partially hydrophobated) silicasB through E as Experimental rubber Samples B through E.

Control rubber Sample A was prepared with untreated precipitated silicaA as Zeosil 1165MP™ from Solvay which was not hydrophobated and isconsidered herein as being a reactive precipitated silica through itshydroxyl groups.

Experimental rubber Samples B through E were prepared with the abovereferenced partially pre-hydrophobated precipitated silicas B through E.

Experimental rubber Samples F and G were prepared with chemicallytreated silica obtained as Agilion 400™ from PPG comprised of anprecipitated silica treated with an alkoxyorganomercaptosilane.

The rubber compositions were prepared by mixing diene-based elastomersand compounding ingredients including precipitated silicas in a firstnon-productive mixing step, or stage, (NP) in an internal rubber mixerfor about 4 minutes to a temperature of about 160° C. The resultingrubber mixtures were dumped from the mixer and allowed to cool andsubsequently mixed in an internal rubber mixer with a sulfur and sulfurcure accelerator(s) to a temperature of about 110° C. as a productivemixing step, or stage (P).

The basic formulation for the rubber Samples is illustrated in thefollowing Table 1 and expressed in terms of parts by weight per hundredparts by weight rubber (phr) unless otherwise indicated.

TABLE 1 phr Non-Productive Mixing Stage (NP) Styrene/butadiene rubber¹70 Cis 1,4-polybutadiene rubber² 30 Rubber reinforcing carbon black(N330)³ 5.2 Fatty acid⁴ 3 Antioxidant, amine based 2 Rubber processingoil 20 Wax, microcrystalline 1.5 Silica coupling agent⁵ 5.2 (control)and 2   Precipitated or partially pre-hydrophobated 65 precipitatedsilica Productive Mixing Stage (P) Zinc oxide 1.5 Sulfur 1.5 (control)and 1.7 Sulfur cure accelerator(s)⁶ 3 ¹Organic solvent solutionpolymerization prepared styrene/butadiene rubber having a bound styrenecontent of about 16 percent as SLF16S42 ™ from The Goodyear Tire &Rubber Company ²Cis 1,4-polybutadiene rubber as Budene ™ 1207 from TheGoodyear Tire & Rubber Company ³Rubber reinforcing carbon black as N330,an ASTM designation ⁴Fatty acid comprised of stearic, palmitic and oleicacids ⁵Silica coupling agent as Si266 a liquidbis(3-triethoxysilylpropyl) polysulfide having an average of from about2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge⁶Sulfur cure accelerator(s) as sulphenamide and diphenylguanidine

Samples of the rubber compositions were prepared by blending theingredients in an internal rubber mixer using two separate, sequentialmixing stages, or steps, namely a first non-productive mixing stage (NP)to a relatively high temperature followed by a second, productive,mixing stage (PR) to a significantly lower mixing temperature in whichthe sulfur and sulfur cure accelerator were added. Such rubber mixingprocedure is well known to those having skill in such art.

For the non-productive mixing stage (NP), the ingredients were mixed forabout 4 minutes to an autogeneously generated temperature via the highshear mixing in the internal rubber mixer to a drop temperature of about160° C. at which the mixed rubber is “dropped” or removed from theinternal rubber mixer. The batch of mixed rubber is sheeted out andallowed to cool to a temperature below 40° C. The batch is then mixed ina productive mixing stage (PR), in which free sulfur and vulcanizationaccelerator(s) are added, for a period of about 2 minutes to a droptemperature of about 100° C.

The cure behavior and various cured physical properties of therespective Samples are shown in the following Table 2. For the curedrubber Samples, the Samples were individually cured for about 30 minutesto a temperature of about 150° C.

TABLE 2 Samples Control Experimental A B C D E F G Silica coupling agent5 2 2 2 2 0 2 Precipitated silica (A) 65 0 0 0 0 0 0Trimethylchlorosilane treated silica 0 65 0 0 0 0 0 (Silica B)Trichloropropyosilane treated silica 0 0 65 0 0 0 0 (Silica C)Trichlorooctyl treated silica (Silica D) 0 0 0 65 0 0 0Trichlorooctadecyl treated silica (Silica E) 0 0 0 0 65 0 0 Commercialtreated silica (Silica F) 0 0 0 0 0 65 65 Properties RPA (Rubber ProcessAnalyzer) Storage modulus (G′) Uncured rubber 100° C., 1 Hz, kPa 179 171212 138 111 166 167 Cured rubber 150° C., 11 Hz, 10%, kPa 1095 1259 14671107 802 872 872 Tan delta, 100° C., 10% strain 0.087 0.077 0.83 0.090.76 0.76 0.083 Curing Information Delta torque (dNm) 16 18 19 16 11 2011 Physical Properties (Stress Strain) Tensile strength (MPa) 15 11 11 97 11 11 Ultimate elongation (%) 510 457 409 507 557 431 390 100%modulus, ring, (MPa) 1.7 2 2.3 1.5 1.2 1.5 1.7 300% modulus, ring (MPa)7.2 6.8 7.9 4.8 3.5 6.7 7.85

From Table 2 it can be seen that the cured rubber G′ values for theExperimental rubber Samples B, C and D (using the partiallypre-hydrophobated precipitated silica) were significantly greater thanthe G′ values for Control rubber Sample A (using the untreatedprecipitated silica), wherein the G′ values for Experimental rubberSamples D and E (using the octyl silane and octadecyl silane partiallyhydrophobated precipitated silica) were significantly lower than the G′value for Control rubber Sample A. Possibly the longer alkyl chains ofthe alkylsilanes used for partially pre-hydrophobated Silicas D and Emay prevent or retard some network formation between the residualhydroxyl groups of the partially hydrophobated precipitated silica andsilica coupler and cross linked elastomer network.

The cured G′ at 10 percent strain values (low strain values) of therubber Samples may sometimes be referred to as “low strain stiffness”values. The higher low strain stiffness of Experimental rubber SamplesB, C and D (as compared to Control rubber Sample A) is considered to bean important predictive handling performance indicator for a tire treadof such rubber composition, with a higher G′ value considered to be apredictor of better handling performance of the tire tread.

In contrast, the Experimental rubber Samples F and G with thealkoxyorganomercaptosilane treated precipitated silica F havesignificantly lower comparative G′ values and thereby a significantlylower comparative predictive handling performance indicator for a tiretread of such rubber composition.

This is considered to be a surprising discovery. It is apparent that thehydrophobated precipitated silica F contains only minimal or minimallyaccessible residual hydroxyl groups.

Further, is it surprisingly seen that the RPA values at low 10 percentstrain for Experimental rubber Samples B, C and D, containing thecoupled alkyl silane partially pre-hydrophobated silicas B, C and D withonly 2 phr of the silica coupler:

(A) somewhat match the low strain tan delta value for Control rubberSample A containing the non-hydrophobated precipitated silica A with itsmuch higher reactive silica coupler concentration of 5 phr, and

(B) have significantly higher cured G′ values than Samples F and G whichcontain chemically treated silica F.

It is important to appreciate that Experimental rubber Samples F and Gcontain a commercially chemically treated precipitated silica wherein itis considered that hydroxyl groups (silanol groups) on the precipitatedsilica are either previously reacted or not accessible for furtherreaction in the rubber composition. In particular, Experimental rubberSample G had silica coupler added to it during mixing whereasExperimental rubber Sample G did not contain an added silica coupler.The indicated physical properties for Experimental rubber Sample G withadded coupler exhibited little to no change as compared to Experimentalrubber Sample F. This demonstrates that if the silanol (hydroxyl) groupson the treated (hydrophobated) silica are not available (e.g.pre-reacted) or not accessible for further reaction as evidenced by verylittle change in cured rubber properties occurring by addition of thesilica coupling agent.

This discovery is considered as being important in a sense thathysteresis was maintained or reduced (evidenced by maintenance orreduction in tan delta values) for rubber Samples B, C and D by simplyusing a partially pre-hydrophobated precipitated silica to promote acombination of dispersion of the precipitated silica in the rubbercomposition and reinforcement of the rubber composition by reaction of asilica coupler with residual hydroxyl groups on the partiallyhydrophobated precipitated silica, particularly by using only a verysmall silica coupling agent being added to the rubber composition toreact with the residual hydroxyl groups on the partiallypre-hydrophobated precipitated silica.

Evaluation of Residual Hydroxyl Groups on Partially HydrophobatedPrecipitated Silica

The presence of hydroxyl groups was evaluated for both untreatedprecipitated silica A and partially pre-hydrophobated precipitatedsilicas B through D. The evaluation was conducted by NMR analysis(Nuclear Magnetic Resonance analysis, Si²⁹ CPMAS NMR).

As indicated, silica Control Sample A is an untreated precipitatedsilica as Zeosil 1165MP™ from Solvay.

Silica Experimental Sample B is Zeosil 1165MP™ precipitated silica Apartially hydrophobated with trimethylchlorosilane as previouslyreferred to in this Example.

Silica Experimental Sample C is Zeosil 1165MP™ precipitated silicapartially hydrophobated with trichloropropylsilane as previouslyreferred to in this Example.

Silica Experimental Sample D is Zeosil 1165MP™ precipitated silicapartially hydrophobated with trichlorooctylsilane as previously referredto in this Example.

In the following Table 3, results of the NMR evaluation are presentedfor the Control untreated precipitated silica A and Experimentalpartially hydrophobated precipitated silicas B, C and D for theirhydroxyl contents as Q1, Q2 and Q3 structures from the NMR analysis. TheQ4 structure is not an hydroxyl containing structure.

The reported Q1 structure represents the presence of —Si—(OSi)(OH)₃.

The reported Q2 structure represents the presence of —Si—(OSi)₂(OH)₂.

The reported Q3 structure represents the presence of —Si—(OSi)₃(OH).

The reported Q4 structure represents the presence of —Si—(OSi)₄.

The reported T1 structure represents the presence of C—Si—(OSi)(OH/ET)₂.

The reported T2 structure represents the presence of C—Si—(OSi)₂(OH/Et).

The reported T3 structure represents the presence of C—Si—(OSi)₃.

Control Silica A is Zeosil 1165MP™, a precipitated silica from Solvay

Experimental Silica B is Silica A partially hydrophobated withTrimethylchlorosilane

Experimental Silica C, is Silica A partially hydrophobated withTrichloropropyosilane

Experimental Silica D, is Silica A partially hydrophobated withTrichlorooctylsilane

TABLE 3 Control Silica Experimental Silica Silica Structures A B C D Q1—Si—(OSi)(OH)₃ 2 0 0 0 Q2 —Si—(OSi)₂(OH)₂ 13 6 6 7 Q3 —Si—(OSi)₃(OH) 6547 44 58 Q4 —Si—(OSi)₄ 20 20 23 21 T1 C—Si—(OSi)(OH/Et)₂ 0 0.7 0.1 0.4T2 C—Si—(OSi)2(OH/Et) 0 12 10 8 T3 C—Si—(OSi)₃ 0 14 18 6

As indicated, the percent of hydroxyl groups on precipitated silicasamples is measured by Si²⁹ CPMAS NMR.

The Q1 through Q3 structures in Table 3 report the presence of originalhydroxyl group structures on the precipitated silica A and residualhydroxyl group structures on partially hydrophobated silicas B, C and D.

It can be seen from Table 3 that a large percentage of the originalhydroxyl (OH) groups remain on silicas B through D after partialhydrophobation of the original untreated precipitated silica A,particularly of the —Si—(OSi)₂(OH)₂, —Si—(OSi)₃(OH) and —Si—(OSi)₄configurations or structures. Such remaining hydroxyl groups aresometimes referred to herein as residual hydroxyl groups.

It can further be seen that a large content of remaining, or residual,unreacted hydroxyl group structures is of the —Si—(OSi)₃(OH) structurewhich ranged from about 70 to about 90 percent of its originalstructural content, as well as the —Si—(OSi)₂(OH)₂ structure whichrepresented about 50 percent of its original structural content, whichrepresent residual hydroxyl groups for eventual reaction with silicacoupler in situ within the rubber composition. With such residual(remaining) active hydroxyl contents, it can be concluded that thisevaluation effectively provided a partial hydrophobation of theprecipitated silica with the alkylsilane.

The intent of this Example was accomplished to both partiallypre-hydrophobate the precipitated silica to promote its dispersibilityin the rubber composition yet leave a significant content of residualhydroxyl groups on the precipitated silica unreacted and therebyavailable and accessible to react with a silica coupler in situ withinthe rubber composition to both “fix”, or stabilize, the dispersion ofprecipitated silica within the rubber composition and also to providefiller reinforcement (coupled precipitated silica reinforcement to therubber composition) for the rubber composition.

It is concluded that this evaluation was successful in partiallypre-hydrophobating the precipitated silica with an alkylsilane in a formof halogenated (chlorinated) alkylsilane in a manner to leave asignificant portion of the hydroxyl groups of the precipitated silicaunreacted and thereby available for subsequent reaction with a silicacoupling agent with which a silica coupling agent successfully reactedwith the residual hydroxyl groups of the pre-hydrophobated precipitatedsilica.

EXAMPLE II Preparation and Use of Partially of In-Situ Pre-HydrophobatedSilica With Alkoxysilane

Partially hydrophobated precipitated silica is prepared by reacting analkoxyalkylsilane with precipitated silica through hydroxyl groups onthe precipitated silica as reported in the following Table B.

TABLE B Precipitated Silica Alkoxyalkylsilane Silica H (notpre-hydrophobated) None Silica I (pre-hydrophobated silica H)OctyltriethoxysilanePreparation of Silica I: Octyltriethoxysilane In-Situ HydrophobatedPrecipitated Silica

The in-situ hydrophobation of a Control precipitated Silica H as Zeosil1165MP™ from Solvay to form Experimental partially pre-hydrophobatedSilica I was carried out in an internal rubber mixer using a separateinitial non-productive mix cycle in which the rubber, silica,hydrophobating agent, and other non-productive ingredients are addedtogether in the mixer and mixed for about 4 minutes to a droptemperature of about 160° C. A second separate non-productive mix cycleis used to subsequently add the coupling agent to the rubber containingthe partially pre-hydrophobated silica. This mix cycle is carried outfor about 4 minutes with a drop temperature of about 160° C. The finalmix stage is a normal productive mix cycle, in which free sulfur andvulcanization accelerator(s) are added, for a period of about 2 minutesto a drop temperature of about 100° C.

The basic formulation for the Experimental rubber Sample I containingExperimental partially pre-hydrophobated Silica I is illustrated in thefollowing Table 4 and expressed in terms of parts by weight per hundredparts by weight rubber (phr) unless otherwise indicated.

TABLE 4 phr Non-Productive Mixing Stage (NP1) Styrene/butadiene rubber¹100 Rubber reinforcing carbon black (N330)² 4 Fatty acid³ 3 Antioxidant,amine based 2 Rubber processing oil 25 Wax, microcrystalline 1.5 Silicahydrophobating agent⁴ 0, 6.4 Silica I (partially hydrophobatedprecipitated Silica H) 80 Non-Productive Mixing Stage (NP2) Silicacoupling agent⁵ 6.4 Productive Mixing Stage (P) 1.5 Zinc oxide Sulfur1.7 Sulfur cure accelerator(s)⁶ 4.7 ¹Organic solvent solutionpolymerization prepared functionalized styrene/butadiene rubber from theTrinseo Company as SPRINTAN SLR 4602 understood to contain functionalgroups comprised of at last one of siloxy and thiol groups ²Rubberreinforcing carbon black as N330, an ASTM designation ³Fatty acidcomprised of stearic, palmitic and oleic acids ⁴octyltriethoxysilane⁵Silica coupling agent as Si266 a liquid bis(3-triethoxysilylpropyl)polysulfide having an average of from about 2 to about 2.6 connectingsulfur atoms in its polysulfidic bridge ⁶Sulfur cure accelerator(s) assulphenamide and diphenylguanidine

The cure behavior and various cured physical properties of therespective Samples are shown in the following Table 5. For the curedrubber Samples, the Samples were individually cured for about 30 minutesto a temperature of about 150° C.

TABLE 5 Samples Control H Experimental I Precipitated silica (H) 80 0Silica I (partially hydrophobated Silica H) 0 80 Silica coupling agent6.4 6.4 Properties RPA (Rubber Processing Analyzer) Storage modulus (G′)Uncured rubber 100° C., 1 Hz, kPa 288 228 Cured rubber 150° C., 11 Hz,10%, kPa 1274 1313 Tan delta, 100° C., 10% strain 0.092 0.063 CuringInformation (RPA, 150° C.) Delta torque (dNm) 7.2 9.5 Zwick Rebound At23° C. (%) 33 37 At 100° C. (%) 70 71 Physical Properties (StressStrain) Ultimate elongation (%) 453 424 100% modulus, ring, (MPa) 2 2300% modulus, ring (MPa) 11 10

The representative data shown in Table 5 demonstrates the advantages ofpre-partially hydrophobating the precipitated silica in situ within therubber composition prior to and separate from reaction of its residualhydroxyl groups with a silica coupler.

In this Example, the amount of coupling agent added is the same for therubber composition (rubber Sample I) containing the pre-hydrophobatedsilica (Silica I) and the control rubber Sample H containing theprecipitated silica (Silica H) without such pre-partial hydrophobation.

The data in Table 5 shows a lower uncured G′ for the rubber composition(rubber Sample I) with the pre-partially hydrophobated precipitatedsilica (Silica I) compared to the control rubber Sample (H) containingthe Silica H which was not pre-hydrophobated. This lower uncured G′value is indicative of an easier to process uncured rubber composition.The cured G′ at 10% strain (a low strain stiffness) is higher for theExperimental rubber composition Sample I which contains thepre-partially hydrophobated silica. This increased cured low strainstiffness value for the rubber composition containing the pre-partiallyhydrophobated silica (rubber Sample I) is an indicator for improved tirehandling for a tire with a tread of such rubber composition. The curedtan delta value at 10 percent strain is lower for the rubber composition(rubber Sample I) containing the pre-partially hydrophobated silica(Silica I) as compared to the control rubber composition (rubber SampleH) containing the precipitated silica (Silica H) which has not beenpre-hydrophobated. This lower tan delta value is a predictor of a tirewith lower rolling resistance with a tread of such rubber composition.

The rebound value at room temperature is higher for the rubbercomposition (rubber Sample I) containing the pre-partially hydrophobatedprecipitated silica (Silica I) compared the rubber composition (rubberSample H) containing the precipitated silica (Silica H) which has notbeen pre-hydrophobated. The higher rebound value is another predictor ofa tire with lower rolling resistance having a tread of such rubbercomposition.

The reported Stress-Strain properties for both the rubber composition(rubber Sample I) containing the pre-partially hydrophobated silica andthe control rubber composition (rubber Sample H) containing theprecipitated silica which has not been hydrophobated are very similar,indicating that the toughness or durability of the cured rubbercompositions are similar. This is important to recognize becausegenerally when a rubber composition has a higher stiffness value (higherG′ value or lower tan delta value) and lower hysteresis value (higherrebound value) as is seen in Table 5 for Experimental rubber Sample Icompared to Control rubber Sample H, the toughness of the rubbercomposition (for Experimental rubber Sample I) would be expected to belower. For Experimental rubber Sample I, however, the similar curedrubber tensile properties indicate similar toughness for Experimentalrubber Sample I and Control rubber Sample H. This observation was anunexpected benefit of Experimental rubber Sample I.

It is thereby concluded that this evaluation was successful in partiallypre-hydrophobating the precipitated silica with an alkylsilane in a formof alkoxyalkylsilane in situ within the rubber composition in a mannerto leave a sufficient portion of the hydroxyl groups of the precipitatedsilica unreacted (residual hydroxyl groups) and thereby available forsubsequent and separate reaction with a silica coupling agent with theresidual hydroxyl groups of the partially pre-hydrophobated precipitatedsilica to promote reinforcement of the rubber composition.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A method which comprises: (A) providing adispersion of a partially pre-hydrophobated precipitated silica in arubber composition containing at least one conjugated diene basedelastomer and a combination of precipitated silica and rubberreinforcing carbon black, which consists of reacting said dispersedprecipitated silica with triethoxyoctylsilane in situ within said rubbercomposition to thereby provide a partially pre-hydrophobatedprecipitated silica containing residual hydroxyl groups; (B) stabilizingsaid dispersion of partially pre-hydrophobated precipitated silicawithin said rubber composition and reinforcing said rubber compositionby subsequently reacting a silica coupling agent with said residualhydroxyl groups of said partially pre-hydrophobated precipitated silicain situ within the rubber composition, wherein said silica couplingagent consists of a bis(3-triethoxysilylpropyl) polysulfide containingan average in a range of 2 to about 2.6 sulfur atoms in its connectingbridge.
 2. A rubber composition prepared by the method of claim
 1. 3. Asulfur cured rubber composition of claim
 2. 4. A tire having a componentcomprised of the rubber composition of claim 3.